Even if segwit is activated, that doesn't mean a particular web site will accept witness transactions. So wallets will need to support both for some time.
AFAIU, non-segwit-supporting wallets will still recognize transactions with segwit inputs. So no need keep creating P2PKH addresses in order to be able to pay to non-segwit wallets
I need to generate P2PKH addresses for non-segwit wallets sending coins to me (the generated addresses are for my private keys). You are correct that non-segwit wallets should handle witness transactions since they will receive them in legacy format.